Why are there green lights under escalators?

Why are there green lights under escalators? Should I start believing in Escalator Trolls? Am I seeing the Otis borealis? Or do I just have a brain tumor? Please--the straight dop

— John Sandel, Chicago

Cecil replies:

John, please, get a grip. Escalator companies put lights under the steps near the top and bottom of the escalator in order to silhouette the edges of each step. The improved visibility is supposed to help you avoid stumbling, or worse, as the step slides against its neighbors on reaching (or leaving) the landing area. The yellow stripe you see on the edge of the steps on some escalators performs a similar function. The lights are part of a code of standards for escalators devised by the American Society of Mechanical Engineers and since adopted by many cities and states. As for why they're green, as opposed to, say, lavender, nobody at ASME could remember. But presumably it was to cut down on glare.